Since the introduction of the Internet and digital audio data coding and compression standards, such as the MPEG or MP3 standards, the circulation of illegal copies of musical works has substantially increased. Recently, file exchange services have been set up which are accessible through the Internet. These services allow software to be downloaded so that any user of the Internet possessing a computer can access file lists to download them, and in exchange, to offer free access to certain files stored on the user's computer hard disk. The references and access path are inserted for this purpose in one of these lists. These services seem to have enjoyed great success among Internet users, who may thus set up, at a reduced price, a personal library of musical or video works, and also software. These illegal copies of works have therefore increased to such a point that they amount to several million dollars per year or more.
For controlling the distribution of digital documents, it has already been proposed to use techniques by which a customer may examine a catalog of documents accessible through a public digital data transmission network, and select documents to purchase. Software installed on the client terminal sends in encrypted form, identification information of the customer's credit card to a distributor organization which, in turn, transmits the selected documents to the customer, also in encrypted form. The software installed on the customer's terminal then uses a secret key to decrypt the received documents so that they can be used.
However, even if the document is protected through encryption during its transmission to the customer, subsequent unauthorized distribution of the latter cannot be prevented once it has been decrypted by the customer. To address this problem, there has also been proposed a technique according to which a password is sold to the customer for decrypting a document loaded onto a document playback apparatus. This password can only be used on the customer's machine or only by the customer as a complement of specific biometric information relating to the customer. Even if the encrypted document may be distributed to other persons, the customer's password and the biometric information do not allow the document to be decrypted.
A distribution system that distributes documents in encrypted form, wherein the users may purchase copy licenses for those documents which are stored in a personal chip card made available to each user, has also been contemplated. This approach is described, for example, in U.S. Pat. Nos. 5,754,548 and 6,035,239.
Since the documents are encrypted, they may freely circulate, in particular, over the Internet. For copying such a document, such as copying the musical work it contains, for example, the user must possess an appropriate reader capable of reading the encrypted contents of the document, and reading information pertaining to the license which is stored in the chip card. This information is used for decrypting the document contents. Such a reader is described in WO 98/42098 and U.S. Pat. No. 5,754,648, for example.
For this purpose, a number of encryption techniques are used for authenticating the reader and the chip card and for decrypting the document. To make a “pirate” reader, it is therefore required that such a reader may authenticate itself as an authorized reader. For this purpose, a private key is needed which corresponds to a certified public reader key. Each reader possibly has a unique private key. The main loophole in this system appears when someone manages to obtain the private key of an authorized reader to make a pirate reader. In this case, it is possible by purchasing licenses to decrypt protected documents and circulate the decrypted documents. It is also possible to create software that may be circulated over the Internet enabling anyone having a computer and a chip card reader to extract the licenses stored on a chip card, decrypt the corresponding encrypted documents that are freely circulated, and freely circulate the decrypted documents.
On the other hand, a number of techniques are available for inserting information into chips to make them less likely to be accessible. However, these techniques are not entirely secure and may not take into account future technologies that pirates might be using. In addition, these techniques are not easily applicable to readers. Readers are systems substantially more sophisticated than chip cards since they comprise a processor having more inputs and outputs, and which are not dedicated to security, contrary to the chips in chip cards.
As opposed to chip card applications, such as in the fields of banking and mobile telephony, the above described secure document circulation technique uses chip cards in readers that are entirely disconnected from a possible centralized system. Fraud thus cannot be as easily detected as in applications using a centralized system that may deactivate a chip card previously detected to be fraudulent. Even if recovering the private key of such a document reader amounts to several months of work, this operation may be carried out in an exclusively private way. Once the private key of a reader has been obtained, the security offered by the system can no longer be ensured.